Positioning systems are widely used to estimate a receiver's location using positioning signals the receiver receives from one or more types of beacons (e.g. terrestrial transmitters or satellites). Positioning signals transmitted from satellites can have relatively low power levels, which makes those positioning signals susceptible to interference. By contrast, positioning signals from terrestrial transmitters often reach a receiver at higher power levels. However, the frequencies used to transmit such terrestrial positioning signals are not subject to the same use restrictions as more conventional positioning system signals like those from satellites. Therefore, there is a higher likelihood that other systems may be transmitting energy that appears as interference to a receiver that receives terrestrial positioning signals.
The presence of interfering signals in a frequency bandwidth of interest is a serious problem for receivers. In time-of-arrival (TOA) positioning systems, this problem poses a considerable threat to the quality of a position estimate made by the receiver. Equipment that emits weak signals within the passband used by receivers can be a major source of interference to a receiver, even when the interference may not have a predictable time and/or frequency pattern. If unsuppressed, such interference may severely compromise the integrity of the position estimate computed by the receiver as well as compromise other aspects of signal acquisition and system time synchronization. Therefore, it would be desirable to have an interference tolerant receiver.